1. Field of the Invention
This invention relates to integrated circuit packaging technology, and more particularly, to a method of singulating a combined batch of small-scale integrated circuit package units, such as TFBGA (Thin & Fine Ball Grid Array) or QFN (Quad Flat Non-leaded) package units, that are constructed on a single matrix base, without leaving remnant portions of provisional bars, such as electroplating bars or connect bars, in the singulated package units that would otherwise cause short-circuiting to the enclosed semi-conductor chips.
2. Description of Related Art
Small-scale integrated circuit packages are typically fabricated in batch on a single base predefined with a matrix of package sites, each package site being used for the fabrication of one single package unit. After encapsulation is completed, it is required to performed a singulation process so as to singulate each individual package unit from the matrix base. TFBGA (Thin & Fine Ball Grid Array) and QFN (Quad Flat Non-leaded) packages, are typically fabricated in this way.
In the case of TFBGA, a substrate predefined with a matrix of package sites (hereinafter referred to as "matrix substrate") is used for the fabrication of a batch of TFBGA package units. The TFBGA matrix substrate is typically formed with a grid-like electroplating bar along the borderlines of the package sites, for the purpose of facilitating the required electroplating to the electrically-conductive traces on the TFBGA matrix substrate. The final singulation process is typically performed by cutting into the provisional electroplating bar, so that it can be incidentally cut away while singulating individual TFBGA package units.
In the case of QFN, a leadframe predefined with matrix of package sites (hereinafter referred to as "matrix leadframe") is used for the fabrication of a batch of QFN package units. The QFN matrix substrate is typically formed with a grid-like connect bar along the borderlines of the package sites, for the purpose of connecting the inner leads of the leadframe together before being singulated. The final singulation process is typically performed by cutting into the provisional connect bar, so that it can be incidentally cut away while singulating individual QFN package units.
One problem in the singulation of TFBGA and QFN package units, however, is that, if the cutting is misaligned, it would undesirably leave remnant portions of the provisional electroplating bars or connect bars in the singulated package units, thus resulting in short-circuiting between the electrically-conductive traces (in the case of TFBGA) or inner leads (in the case of QFN), which would make the enclosed semiconductor chips inoperable. As a result, the finished package units will be regarded as defective ones. This problem is illustrated depicted in the following with reference to FIGS. 1A-1E for TFBGA and FIGS. 2A-2E for QFN.
Conventional TFBGA Singulation (FIGS. 1A-1E)
FIG. 1A shows a schematic plan view of a TFBGA matrix substrate 100 used for TFBGA fabrication; and FIG. 1B shows a schematic sectional view of an unsingulated batch of TFBGA package units constructed on the TFBGA matrix substrate 100 (note that FIGS. 1A-1B are simplified to show only a small number of circuit components for demonstrative purpose; the actual circuit layout may be much more complex.)
As shown in FIG. 1A, the TFBGA matrix substrate 100 is predefined with a matrix of package sites 110 (only two are fully shown in FIG. 1A) used for the fabrication of a batch of TFBGA package units thereon. The package sites 110 are delimited from each other by a grid-like electroplating bar 120 which is formed along the borderlines of the package sites 110, and are each formed with a plurality of electrically-conductive traces 130 on the front side thereof. To facilitate electroplating process, these electrically-conductive traces 130 are all connected to the electroplating bar 120. Further, the package sites 110 are each mounted with at least one semiconductor chip 140 in the center of the front side thereof and electrically coupled to the electrically-conductive traces 130.
Further, as shown in FIG. 1B, a continuous encapsulation body 150 is molded to encapsulate all the semiconductor chips 140 over the TFBGA matrix substrate 100; and a plurality of solder balls 160 are implanted on the back side of the TFBGA matrix substrate 100. The electrically-conductive traces 130 on the front side of the TFBGA matrix substrate 100 are connected through electrically-conductive plugs (not shown) to the solder balls 160 on the back side of the same, for the purpose of electrically connecting the semiconductor chips 140 to the solder balls 160.
Before mounting the semiconductor chips 140, it is required to perform an electroplating process so as to electroplate an electrically-conductive material, such as nickel-gold (Ni-Au), onto the electrically-conductive traces 130. During the electroplating process, the electroplating electrical current is applied to the electroplating bar 120, so that the electrical current can be then concurrently distributed by the electroplating bar 120 to each of the electrically-conductive traces 130. After the electroplating process is completed, the electroplating bar 120 becomes a useless structure; and therefore, it can be subsequently cut away during the singulation process.
During the singulation process, a cutting blade 170 of a fixed width W greater than the width of the electroplating bar 120 is used to cut into the TFBGA matrix substrate 100 and the encapsulation body 150 along the crosswise singulation lines SL.sub.X and lengthwise singulation lines SL.sub.Y shown as dotted lines in FIGS. 1A-1B, for the purpose of singulating the combined batch of TFBGA package units constructed together on the TFBGA matrix substrate 100 into individual ones. The crosswise and lengthwise singulation lines SL.sub.X, SL.sub.Y should be precisely aligned to cover the entire width of the electroplating bar 120 within the cutting range of the cutting blade 170.
As further shown in FIG. 1C, the cutting by the cutting blade 170 is carried out all the way into the TFBGA matrix substrate 100 and the encapsulation body 150 along the crosswise and lengthwise singulation lines SL.sub.X, SL.sub.Y. Through this singulation process, the combined batch of TFBGA package units are singulated into individual ones.
One drawback to the forgoing TFBGA singulation, however, is that, since the TFBGA matrix substrate 100 is typically very small in size, where the electroplating bar 120 is typically from 0.05 mm to 0.1 mm (millimeter) in width, typically 0.07 mm, and the cutting blade 170 used in the singulation process is typically 0.3 mm in width, In this case, the cutting tolerance is only (0.3-0.07)2=0.115 mm. In other words, the cutting blade 170 should be highly precisely aligned to the electroplating bar 120 along the crosswise and lengthwise singulation lines SL.sub.X, SL.sub.Y shown in FIGS. 1A-1B; otherwise, if the misalignment exceeds 0.115 mm, it would cause the problem of trace short-circuits.
As shown in FIG. 1D, in the event that the cutting blade 170 is misaligned with respect to a lengthwise portion of the electroplating bar 120, then an edge part 1230a of the electroplating bar 120 will be uncovered by the lengthwise singulation lines SL.sub.Y. As a result, the uncovered edge part 120a of the electroplating bar 120 is beyond the cutting range of the cutting blade 170.
As further shown in FIG. 1E, the case of FIG. 1D would cause the uncovered edge part 120a of the original electroplating bar 120 to remain over the edge of the singulated package site 110, thus undesirably causing the electrically-conductive traces 130 to be short-circuited to each other. As a result, this singulated TFBGA package unit would be regarded as defective.
One solution to the foregoing problem is to use a cutting blade of a greater width to perform the singulation process. This solution, however, is quite unfeasible since it will cut away a larger part of the TFBGA matrix substrate 100 and the encapsulation body 150, thus reducing the already very small circuit layout area of each package site.
Another solution is to repeatedly check the result of each pass of cutting; and if the electroplating bar 120 is not entirely cutaway, the cutting blade 170 is realigned to perform another pass of cutting until the electroplating bar 120 is entirely cut away. This solution, however, is quite laborious and time-consuming.
Conventional QFN Singulation (FIGS. 2A-2E)
FIG. 2A shows a schematic plan view of a QFN matrix leadframe 200 used for QFN fabrication; and FIG. 2B shows a schematic sectional view of an unsingulated batch of TFBGA package units constructed on the QFN matrix leadframe 200 (note that FIGS. 2A-2B are simplified to show only a small number of circuit components for demonstrative purpose; the actual circuit layout may be much more complex.)
As shown in FIG. 2A the QFN matrix leadframe 200 is predefined with a matrix of package sites 210 (only two are fully shown in FIG. 2A) used for the fabrication of a batch of QFN package units thereon. These package sites 210 are delimited from each other by a grid-like connect bar 220 which is formed along the borderlines of the package sites 210, and each include a die pad 231 and a plurality of inner leads 232 which are all connected to the grid-like connect bar 220 so that these inner leads 232 can be held together before being singulated. Further, the package sites 210 are each mounted with at least one semiconductor chip 240 on the die pad 231 thereof and electrically connected by means of a set of bonding wires 241 to the inner leads 232.
As further shown in FIG. 2B, a continuous encapsulation body 250 is molded to encapsulate all the semiconductor chips 240 over the QFN matrix leadframe 200. During subsequent singulation process, a cutting blade 270 of a fixed width W greater than the width of the connect bar 220 is used to cut into the QFN matrix leadframe 200 and the encapsulation body 250 along the crosswise singulation lines SL.sub.X and lengthwise singulation lines SL.sub.Y shown as dotted lines in FIGS. 2A-2B, for the purpose of singulating the combined batch of QFN package units constructed together on the QFN matrix leadframe 200 into individual ones. The crosswise and lengthwise singulation lines SL.sub.X, SL.sub.Y should be precisely aligned to cover the entire width of the grid-like connect bar 220 within the cutting range of the cutting blade 270.
As further shown in FIG. 2C, the cutting by the cutting blade 270 is carried out all the way into the QFN matrix leadframe 200 and the encapsulation body 250 along the crosswise and lengthwise singulation lines SL.sub.X, SL.sub.Y. Through this singulation process, the combined batch of QFN package units are singulated into individual ones.
As shown in FIG. 2D, in the event that the cutting blade 270 is misaligned to a lengthwise portion of the grid-like connect bar 220, then an edge part 220a of the connect bar 220 will be uncovered by the lengthwise singulation lines SL.sub.Y. As a result, the uncovered edge part 220a of the grid-like connect bar 220 is beyond the cutting range of the cutting blade 270.
As further shown in FIG. 2E, the case of FIG. 2D would cause the uncovered edge part 220a of the original grid-like connect bar 220 to remain over the edge of the singulated package site 210, thus undesirably causing the inner leads 232 to be short-circuited to each other. As a result, this singulated QFN package unit would be regarded as defective.
One solution to the foregoing problem is to use a cutting blade of a greater width to perform the singulation process. This solution, however, is quite unfeasible since it will cut away a larger part of the QFN matrix leadframe 200 and the encapsulation body 250, thus reducing the already very small circuit layout area of each package site.
Another solution is to repeatedly check the result of each pass of cutting; and if the connect bar 220 is not entirely cutaway, the cutting blade 270 is realigned to perform another pass of cutting until the connect bar 220 is entirely cut away. This solution, however, is quite laborious and time-consuming.